Radiation therapy apparatus with selective shielding capability

ABSTRACT

Brachytherapy applicators incorporate various forms of selective shielding devices for controlling the direction and intensity of radiation directed at a patient&#39;s tissue. In some forms the applicators include a retractable sheath, in some a series of retractable fingers. In other forms the applicator, having an inflatable balloon, has a shield which is retractable from a position adjacent to the balloon or retracted from the balloon, or a shield can itself be inflatable, separately or together with the balloon.

BACKGROUND OF THE INVENTION

The invention concerns shielding for radiation therapy sourceapplicators, especially adjustable shielding for dynamic control of aradiation emission pattern.

Several forms of ionizing radiation therapy, particularly brachytherapyin which radiation is administered from a radiation source positionedwithin an anatomical cavity, are delivered using an applicator. Purposesfor use of an applicator may include positioning the source within thecavity, mitigating radiation intensity incident on the cavity wall(radiation intensity decays exponentially with distance from thesource), or tailoring cavity shape to facilitate radiation delivery inaccordance with prescribed therapy parameters. Other purposes may alsoexist. The anatomical cavity may be a natural cavity, or may result fromsurgical intervention, for example as in the case of removal of acancerous lesion.

Some applicators are essentially solid and of fixed configuration inthat their shape doesn't vary during therapy. A typical fixedconfiguration applicator might comprise a catheter or wand, fashionedfor placement within a body cavity, and into which a source, usuallycontained within a catheter, can be positioned. Such an applicator canbe inserted into the body either through a natural orifice, or through asurgical incision or entry. Other forms of applicators may incorporateextensible elements which can be caused to alter shape after insertioninto the body. A common form of the latter is a balloon applicator.Proxima Therapeutics Inc. of Alpharetta, Ga. (now part of CytycCorporation of Marlborough, Mass.) offers extensible applicatorsincorporating balloons. These applicator balloons are generally inflatedwith saline solution so as to attenuate radiation intensity near thesource itself. With such an applicator, the source is ideally confinedwithin a tube or channel within the balloon such that the position ofthe source within the outer skin or surface of the balloon is controlledand known. Preferably the shape of the inflated, extensible surface iscoordinated with the radiation field of the source such that theintensity of radiation delivered just outside the surface of the balloonis uniform, below dangerous levels, but still strong enough to provideeffective therapy.

Traditionally, the strength of the balloon, i.e. its rigidity orconformation under inflation pressure, is chosen such that it shapes ortends to conform the tissues surrounding the cavity to the desired shapeof the balloon as well to the radiation field expected from the source.When these factors can be simultaneously achieved, a uniform or isodoseprescription can be delivered to the innermost tissues forming thecavity. When this is the case, the therapist can be assured of a uniformtherapy throughout the target tissue adjacent the cavity. All too often,however, this condition cannot be produced. Sometimes the cavity cannotbe reshaped such that the radiation intensity outside the balloon isinsufficiently uniform, and cannot deliver a prescribed dose. Shouldthis situation arise, a balloon which conforms to the existing cavitycan be employed, along with other measures to assure delivered doseuniformity. In other instances, radiation-sensitive tissue structuresmay lie within the therapeutic range of the radiation outside theballoon, and would be injured were a therapeutic dose of radiationdelivered. In these instances, the therapist cannot deliver a preferredtreatment unless other measures are taken to avoid over-treatment ofat-risk tissue. It is these “other” measures to which this invention isaddressed.

The radiation source is usually positioned within or near the distal tipof a catheter to facilitate handling of the source and positioning itwithin the applicator. The source may be isotopic in nature or it may beelectronic, producing x-rays which can produce a therapeutic effectsimilar to isotopes. Isotope sources may be essentially point sources,comprising a single isotope “seed”, or they may be linear sources,comprising a series of seed sources, or a wire. When the sources are aseed, or seeds or a wire, they are generally positioned in a catheterfor insertion into the applicator in order to access the anatomicalcavity to be treated. In other applications, the radiation source can bea fluid comprising radioactive material in suspension. This fluid can beused to inflate the extensible element of the applicator.

Radiation from radioisotopes is emitted in a known manner with adecaying intensity measured by the isotopes' half-life—the time at whichhalf of their original intensity remains. Within practical timeconstraints, these parameters for a given radioisotope are fixed andthey cannot be altered thus offering no possibilities for control.Furthermore, radioisotopes emit radiation at a few distinct energybands, radiation from each band having its own ability to penetratetissue and deliver dose. For example, the high-energy band of radiationemitted from ¹⁹²Ir, the most common high dose-rate brachytherapyisotope, penetrates through large thicknesses of shielding materials. Inaddition, isotopes are always “on”, so controlling the output withon/off switching is not possible. Other common and medically relevantradioisotopes also have emission spectra containing high-energycomponents that make selective shielding within a body cavityimpractical due to space considerations. The radiation from theseisotopes will penetrate any practical thickness of shielding material.This high-energy radiation easily penetrates well beyond the target siterequiring therapy, thus delivering radiation to healthy parts of thebody and risks injury. It also puts the therapist at risk, necessitating“bunker” type installations within which therapy can be conducted in theabsence of attending personnel. This is a major disadvantage to the useof isotopic radiation in therapy.

In contrast, with electronically controlled radiation sources, the shapeof the anode and its structure, and any minimal shielding utilized,determines the directionality of the x-rays emitted. Such an x-raysource is described in U.S. Pat. No. 6,319,188, the specification ofwhich is incorporated herein in its entirety by reference. The emittedx-rays from such a source may be emitted isotropically, they may bedirected radially, axially, or a combination thereof. Anode shaping iswell known by those skilled in the art of x-ray generation apparatus.Anode shape, target thickness and target configuration can be used tochange the radiation profile emitted from the miniature x-ray source.Also, miniature x-ray sources capable of producing the therapeuticeffects of high dose rate isotopes only require thin radiation shieldsto selectively block emitted radiation, thus producing a directionallyshaped radiation field. With electronically produced x-rays, theacceleration voltage determines the energy spectrum of the resultingx-rays. The penetration of the x-rays in tissue is directly related tothe energy of the x-rays. The cumulative radiation dose directed at apoint of the lesion may be controlled by x-ray source beam current or by“on” time within the body of the patient. Control of these parametersmay be applied manually, or it can be automated in real-time based onmatching output to a prescribed dose based on sensor feedback to acontroller. An exemplary controlled system is described in co-pendingpatent application Ser. No. 11/394,640, filed Mar. 31, 2006, thedisclosure of which is herein incorporated by reference in its entirety.This ease of control with x-rays and their minimal safety requirementsare significant advantages to the therapist and the patient.

Therefore, in order to provide the therapist the ability to protectradiation-sensitive or normal tissue structures selectively fromtherapeutic dosages prescribed to treat diseased tissue, convenientapparatus and methods are needed which can be adapted to selectivelyshield these at-risk tissues while allowing prescribed dosages toadjacent, diseased tissue. The apparatus and methods of this inventionprovide the therapist this ability.

SUMMARY OF THE INVENTION

This invention comprises an array of shielding apparatus and methodswhich can be applied to solid (non-extensible) radiation therapyapplicators. The invention further comprises apparatus and methods foruse with applicators which incorporate an extensible element orelements, for example balloons. Some shielding embodiments areapplicable to both types of applicator. Furthermore, in addition tobeing applicable to use of miniature x-ray sources for radiationtherapy, they can be used with low dose rate isotopic sources where theemitted radiation can be effectively blocked by application of theshielding embodiments described.

As mentioned above, solid applicators may comprise flexible tubularsheaths or rigid wands, comprised of materials with minimal radiationattenuating properties, through the lumen of which a radiation sourcecan be introduced and advanced into proximity of the tissue to beirradiated. If it is desired to shield a portion of the radiationoutput, radiation attenuating members may be incorporated into thecatheter or applicator design, for example by providing an additionallumen or lumina within the sheath or wand shaft, through which aradiation attenuating member or members may be positioned adjacent theradiation source. By careful placement, the member or members maytherefore be positioned to lie between the source and the tissuestructures to be protected. The radiation attenuating members may be infixed positions within the applicator relative to the catheter and/orsource, or they may be moveable. Furthermore, if a plurality ofattenuating members is employed, the members can be individuallycontrolled or collectively controlled. If, for example, the membersextend to the proximal end of the catheter or wand, control can be byhand manipulation, or by automatically actuated manipulation. Equally,manipulation can be indirect, for example by hydraulic actuation withpressure acting within the member lumen and acting against the proximalend of the member, assuming adequate seal between the member and lumento achieve a piston effect.

If a single, tubular attenuating member is used, it can slide over thesheath or wand, or slide within the radiation source lumen, between thesource and interior surface of the sheath. The attenuating member can betruncated angularly, or otherwise shaped, including comprising a windowat its distal tip so as to produce the radiation output desired. Ifmultiple attenuating members are employed, they can pass throughindividual lumina in the sheath or wand, or can be arrayed within anannular space inside the sheath lumen and outside of the sourcecatheter. Each member may be shaped at its distal end in order tocooperate with adjacent members to produce the shielding effect desired.An exemplary shape of interest is both elongate and arcuate such thatcollectively, an array of adjacent members can be arranged to form atube-like shield of attenuating material about the source within. Suchan arrangement will substantially direct the radiation forward in thedistal direction, with perhaps a lesser amount proximally toward thetherapist (depending on applicator configuration), and very littleradially. Alternatively, one or more of the attenuating “paddles” orfinger-like shield segments can be individually retracted to producecircumferentially limited radiation output, directed radially. Suchretraction can be constant, either open or closed. Equally, it can becyclic, manually driven or automated, and can generate a rotatingradiation path if desired.

Such an array, and the catheter and source, can extend beyond the distalend of the applicator sheath if desired. Proximal of the distal end ofthe sheath, the members or shield sections can transition from elongatearcuate paddles into round, wire-like extensions passing throughapplicator lumina and reaching the proximal end of the sheath, therebypermitting manipulation of the distal “paddles”. The entire assemblycould be operable within the sheath wall. With this arrangement, thedistal end of the sheath or wand could optionally be closed, rather thanopen to the cavity. If distally, axially directed radiation isundesirable in such a case, the distal end of the sheath can be cappedwith radiation attenuating material which is heavily absorptive ofradiation.

Another embodiment of interest is a pair of nesting, attenuating tubesoperating within the lumen of the sheath, and surrounding the sourcecatheter. The distal ends of the two tubes are castellated with sectionscut from the ends such that when properly aligned, the circumferentialshield is complete, blocking radial emission. Relative rotation of thetubes can produce a radial beam or beams of radiation. Alternatively,the tubes can have cooperating windows such that relative rotation opensa desired window or windows for release of radiation. Or, the tubes maybe translated axially relative to one another, such that the axiallength of the windows can be varied. If the relative position of thetubes is arranged to form a fixed window, the tubes may be translatedand rotated to collectively irradiate a desired portion of the cavitytissue. See copending application Ser. No. 11/323,346, filed Dec. 30,2005, the disclosure of which is included herein by reference,describing relatively movable windows in concentric tube shields.

In the embodiments discussed above, the shielding apparatus described isgenerally movable relative to the sheath body or shaft, comprised of asingular or a plurality of cooperating components and is independent of,but coordinated with, movement of the source catheter and source. Theshield can be stationary, with the source movable axially.

In another embodiment, a solid applicator is comprised at leastpartially attenuating material, at least at the distal end of thesheath, so fashioned as to permit a radiation field having preferredshapes and characteristics dependent on the location of the sourcewithin the sheath. As a simple example, a tubular, attenuating shieldingextension can be affixed to the distal end of the applicator sheath. Theinternal diameter of the extension can correspond to that of the sheathsuch that the source may be moved freely through the internal lumen ofthe assembly. The outer diameter of the extension, however, may betapered or stepped, diminishing distally, such that the radiationdelivered radially may be attenuated somewhat when the source ispositioned distally, but more heavily attenuated when the source ispositioned more proximally within the sheath assembly. Similarly, thesolid tubular shield extension may be circumferentially notched orincomplete such that relatively unattenuated radiation emanates radiallywhere portions of the shield are thin or missing, but purposelyattenuated where they are all present. In such a fixed construction, thedistal tip may or may not be blocked by attenuating material as suitsthe situation.

As stated earlier, attenuation apparatus may be fashioned forapplicators with extensible or balloon elements, through which thetherapeutic radiation passes. Most, if not all, of the shieldingembodiments described above for use with solid applicators may beapplied to balloon applicators as well, with the attenuating membersfunctioning within or about the sheath or shaft onto which the balloonis affixed. In other respects, the description of these embodiments issimilar, but the shielding portions of the embodiments operate withinand are enclosed by the balloon. The balloon itself provides additionalshielding opportunities, including opportunities to more precisely shapethe intensity of the radiation field selectively.

When a balloon is being used as part of an applicator, the target zonefor therapeutic radiation is generally a tissue volume all around theinflated balloon extending about one centimeter radially outwards fromthe surface of the balloon. It is this tissue which is generally thoughtto be most susceptible to recurrence of disease, especially cancer. Fortherapeutic purposes, a minimum intensity is required for celldestruction, and this minimum forms the basis for the prescription doseone centimeter outward from the surface of the balloon. As is known tothose of skill in the art, radiation intensity decays exponentially asit passes through matter, therefore the intensity at the surface of theballoon will be greater than at the one centimeter target depth. It isimportant that the intensity at the balloon surface not be substantiallygreater than at target depth, however, since that would be overlydestructive, and might risk injury to adjacent healthy tissue. At thesurface of the source or source catheter, the intensity of the radiationis usually too high for therapeutic use.

Balloon applicator design utilizes the attenuating properties of theinflation medium in the balloon and the balloon membrane itself toattenuate radiation intensity from a high level at the source catheterto manageable intensity at the outer surface of the balloon. This isachieved by manipulation of attenuating properties of the inflationmedium and balloon, and/or by the geometrical size and shape of theballoon. The useful effect of this technique is that the ratio ofradiation intensity incident on the tissue at the balloon surface to theintensity one centimeter outward from the balloon is reduced, implying amore uniform dose throughout the target tissue. This phenomenon iscalled “beam hardening”.

The absorption properties of the balloon membrane itself can be variedto tailor to suit the overall design situation. Balloon materials areusually polymers and are commonly polyurethane, PET, silicone rubber, orsimilar materials well known to those of skill in the art. The materialof most balloon membranes is normally quite transparent to radiation,but their radiation attenuating properties can usually be tailored byloading them with attenuating fillers. Attenuating fillers such asbarium sulfate and metallic particulates can be compounded into theseballoon materials. Other fillers are also well known to those skilled inthe art. The higher the filler loading generally, the more attenuatingthe resultant material, and the more rapid the exponential decay of theradiation incident upon it. In the end, total attenuation of a materialis a function of both its attenuation properties as well as thethickness over which those properties block the path of the radiation.Therefore, a weakly attenuating but thick material may be equallyeffective at shielding tissue from radiation as a thin but stronglyattenuating material.

In addition to material composition modifications to the balloons, theirconstruction can be altered as well. For example, the wall thickness ofthe balloon membrane can be varied selectively during the manufacturingprocess. Thickness variations can result from molding design, or theycan result from fabrication of balloon using materials of dissimilarthicknesses. Fabrication of materials of similar thickness, butdifferent filler loadings may also be used to selectively shieldspecific balloon areas. See also copending application Ser. No.10/683,885 (filed Oct. 13, 2003) and Ser. No. 10/962,247 (filed Oct. 8,2004) regarding attenuating balloons. The disclosures of both copendingapplications are included herein by reference.

As described above, the balloon may serve the further purpose ofmechanically shaping the cavity by virtue of the pressure within theballoon. If the shaped cavity corresponds to the source intensitypattern, uniform dosage as prescribed is a relatively simple matter. Ininstances where the cavity either has a free-form shape or cannot beformed into a preferred shape, a balloon having elastic behavior (cavityfilling) may be preferred in order to avoid air gaps outside the balloonadjacent the tissue forming the cavity. Such balloons may be of many ofthe same but the more elastic of the membrane materials outlined above,but probably with lesser wall thicknesses. Fillers can be similarlycompounded into the material, or fabrication techniques can again beused to tailor attenuation. What is not under control where balloonbehavior is elastic is the distance to target tissue from the source.Care must be taken to assure that the intensity of delivered radiationremains between the prescribed level and the danger level over the totalballoon surface. Thicknesses may also be varied, but the problem becomesvery complex because irregular expansion of the balloon alters themembrane thickness as well as its loading of filler per unit area, andhence its attenuating properties. Generally, the greater the distancethe balloon expands, the thinner the membrane in that area.

In use of either solid or balloon applicators, either those of theinvention, or prior art applicators, it may be desirable to provideshielding for the therapist in the proximal direction along the shaft ofthe wand or catheter. Particularly when the applicator is in use near abody opening, radiation may escape proximally along the shaft out of thepatient toward where the therapist is likely to be positioned. When suchexposure is likely, a local shield may be employed which is mounted onthe applicator shaft to shield in the proximal direction. Thisembodiment may be solid sort of flange, and overlap the body openingsufficiently to block any such radiation effectively. Alternatively, itmay fit within the body opening, forming a radiation seal in concertwith the opening. Further, it may comprise an inflatable elementindependent of or integral with the main inflatable element of theapplicator. Still further, on a balloon applicator, it can comprise ashielding member or attenuating segment at the proximal end of theprimary applicator balloon such that it is automatically deployed whenthe applicator is put into use, and is of adequate scope or projectionto prevent outwardly directed radiation toward the therapist.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of preferredembodiments which, taken in conjunction with the accompanying drawings,illustrate by way of example the principles of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of the tip of a solid applicator with anopen tip, and having a source catheter positioned within emittingaxially directed radiation at the tip.

FIG. 1 b is a perspective view of the embodiment of FIG. 1 a, but withthe source catheter advanced and emitting radiation isotropically.

FIG. 1 c is a perspective view of the tip of the embodiment of FIG. 1 a,but with a closed tip which can be opened by advancement of the sourcecatheter of FIG. 1 a.

FIG. 1 d is a perspective view of the tip of the embodiment of FIG. 1 c,but with the source catheter advanced and emitting radiation.

FIG. 2 a is a perspective view of the tip of a solid applicator having“paddle” shaped shielding elements deployed circumferentially at the tipof the applicator sheath, and showing proximal extensions of theshielding members for axial manipulation of the elements from outsidethe patient, and with an axially shielded source catheter positionedwithin the shielding members.

FIG. 2 b is a perspective view of the applicator tip of the embodimentof FIG. 2 a with two of six shielding elements retracted and partiallyexposing the top side of the source catheter in order to emit radiationradially over a portion of the applicator circumference.

FIG. 2 c is a section taken through the shaft of the applicator of theembodiment of FIG. 2 a.

FIG. 3 a is a perspective view of the tip of a two-part, coaxialattenuation embodiment to be positioned over the source catheter butwithin the sheath lumen, having castellated ends that in this view areso rotated as to act in concert to shield radial radiation completely.

FIG. 3 b is a perspective view of the embodiment of FIG. 3 a, but withthe two parts so rotated as to permit two opposed beams of radiationradially.

FIG. 4 a is a perspective view in partial section of the tip of atwo-part attenuation embodiment, with open tip, to be positioned overthe source catheter, each part having a window and the windows shown sorotated as to block all radial radiation emission.

FIG. 4 b is a perspective view of the embodiment of FIG. 4 a, but withone window rotated and translated such that the window is partiallyopen.

FIG. 4 c is a perspective view of the embodiment of FIG. 4 a, but withthe tip of the inner part capped to prevent radiation emissionsdistally.

FIG. 5 is a perspective view of a one-part attenuation embodiment tooperate within the applicator sheath and over the source catheter,having an angularly truncated distal tip, and with a source cathetershown within, such that directional radiation is provided.

FIG. 6 is a perspective view of another one-part embodiment as in FIG.5, but having a window through which radiation can emanate so as toprovide directional radiation.

FIG. 7 is a cross sectional view of the tip of a one-part attenuatingsheath having a tapered distal tip to provide varied attenuation.

FIG. 8 is a cross sectional view of the tip of a one-part attenuatingsheath having a stepped distal tip to provide varied attenuation.

FIG. 9 is a perspective view of an applicator similar to that of FIG. 1b but including a balloon.

FIG. 10 is a perspective view of an applicator similar to that of FIG. 2b but including a balloon with the applicator affixed to the balloon attwo points.

FIG. 11 is a side elevation view with partial sectioning showing aballoon applicator having a shielding apparatus similar to that of FIG.4 b and with the applicator sheath affixed to the balloon at two points.

FIG. 12 is a side elevation view of a balloon applicator having aone-part shield similar to that of FIG. 5.

FIG. 13 is a side elevation view of a balloon applicator having a onepart shield similar to that of FIG. 6 with the applicator sheath affixedto the balloon at two points.

FIG. 14 is a side elevation view showing two axially shieldingembodiments to attenuate proximally directed radiation, the one at rightbeing a shielding section molded as part of the balloon or affixed onthe balloon during or after balloon manufacture, and the embodiment atleft being a solid attenuating flange with hub mounted slidably on theshaft of the applicator.

FIG. 15 is a side elevation view of a balloon applicator having aninflatable, attenuating balloon collar as an integral part of andproximal to the main applicator balloon.

FIG. 16 is a side elevation view of a balloon applicator and sourcehaving an independently inflatable collar mounted on the shaft of theapplicator.

FIG. 17 is a schematic view of a balloon applicator positioned withinbreast tissue in the vicinity of a bone (rib) wherein the balloon has ashielding segment positioned adjacent to the bone so as to protect thebone from radiation.

FIG. 18 is a schematic view of an applicator and source positionedwithin breast tissue and having a solid flange shield as in FIG. 14positioned on the applicator shaft at the entry into breast tissue.

DESCRIPTION OF PREFERRED EMBODIMENTS

The figures generally illustrate the shielding embodiments of thepresent invention wherein the shielding serves to selectively protectcertain tissue structures while not interfering with prescribedradiation therapy. In the drawings, the straight sheath or shaft of theapplicators illustrated are shown shorter than they would in fact be.Furthermore, balloons are depicted as being transparent in order to moreclearly illustrate apparatus within the balloons.

FIG. 1 a shows a simple, solid, tubular attenuating applicator 10 havingan open end 11, into the lumen of which is inserted a source catheter12. Depending on the source and catheter characteristics, radiation canbe emitted from the distal end. The degree of collimation will depend onthe depth of the source within the applicator lumen. Such an applicatorcan be fashioned from a polymer like polyurethane, polypropylene, or ametal like stainless steel. In general, at least with electronicradiation sources, most metallic shielding totally absorbs any incidentradiation in the range of interest for brachytherapy. If polymeric,attenuation can be controlled by filler additions into the material fromwhich the applicator is made. Typical fillers might include bariumsulfate or tungsten or stainless steel powder. Generally, the greaterthe filler component, the greater the degree of attenuation in theresulting filled material. In design, this applicator need be nothingmore than a tube, perhaps extruded if polymeric, and drawn or machinedif metallic.

FIG. 1 b illustrates how such an applicator 10 as shown in FIG. 1 amight function when the source 13 is advanced to a position distal ofthe end of the applicator shaft. In this case, the radiation is shown asif the source is essentially isotropic, emitting radiation throughoutgenerally a spherical envelope.

FIG. 1 c shows a variation of the applicator 10 of FIG. 1 a, but with aclosed tip which is separated into segments 14 which can hinge out ofthe way of the source catheter 12 as it is advanced. In this way, theembodiment shown is self-closing and can completely close off radiationwhen the catheter is withdrawn within the applicator rather thanemitting radiation distally out of an open tip as in FIG. 1 a. When thesource and catheter are advanced, however, the tip opens by the segmentshinging as shown in FIG. 1 d, permitting radiation emission as in FIG. 1b. This can be accomplished with a polymeric material that tends toretain and to return to a preferred shape as in FIG. 1 c.

FIGS. 2 a-2 e show an applicator 20 having a central lumen 21 forpositioning the source catheter 12 centrally within the applicator 20.The applicator 20 also has satellite lumina 24 for positioning andmanipulating paddle-like attenuation members or fingers 22 positioned inslots 23 within the wall of the shaft or sheath of the applicator tip,into which the paddles can be partially or completely retracted. Paddles22 have rod-like proximal extensions 25 operating in lumina 24 which canbe used to manipulate the paddles or fingers from outside the patient'sbody, as indicated by the axial arrows. Alternatively, the paddles 22and source 13 can function completely within the envelope of theapplicator, never emerging axially from the tip of the applicator. Inthis embodiment, the applicator sheath 20 is fashioned from a polymer asdescribed above, but with minimal attenuating filler, and morepreferably without filler. The paddles are made of filler loaded,attenuating polymer such as that described above. They could also bemetallic. In operation, retraction of selective paddles as shown in FIG.2 b will allow radiation emission in selective sectors around thecircumference of the applicator. When positioned to act in concert, allradial emissions can be blocked or absorbed. Radiation can be sweptrotationally by active use of the shielding members.

FIG. 2 c shows a cross section through the shaft or sheath of theapplicator 12. The lumina 24 for operating the paddles 22 are arrangedas satellites around the central lumen 21 through which the source andits catheter are passed. It must be appreciated that other than paddleshapes can be employed without departing from the scope this invention.

FIG. 3 a depicts a pair castellated tubes 31 and 32 designed to operatewithin the central lumen of the applicator (not shown), but generallysurrounding the source catheter (not shown). When the tubes arepositioned as shown in FIG. 3 a, all radial emission is blocked. Whenpositioned as shown in FIG. 3 b, circumferential segments 33 of theapplicator emit radiation. At intermediate relative rotations, thosesegments are narrower than when fully open, as shown. In the embodimentshown, the castellation notches are rectilinear. They could equally beother shapes to suit a given situation without departing from theinvention. The materials for the two tubes is preferably metallic, oralternatively attenuating polymers containing fillers as describedpreviously.

The embodiment shown in FIGS. 4 a and 4 b generally corresponds to thatof FIGS. 3 a and 3 b, but rather than notches in the ends of the tubes,each tube 41, 42 has a window 43, 44 which can be positioned tocooperatively restrict the beam of radiation allowed to exit theapplicator. The beam can be restricted axially by axial adjustment ofone tube relative to the other, and it can be limited circumferentiallyby relative rotation (see arrows). Depending on the attenuationproperties chosen, the beam can be partially blocked (one tube thicknessof attenuation) or not attenuated (open window). By blocking the end ofone or both tubes, by a disc 45 integral with tube 42 for example, axial(distal) radiation can be blocked as well.

FIGS. 5 and 6 show one-part shield embodiments 50, 60 that comprisetubes which can be manipulated (see arrows) to operate within theapplicator lumen (not shown) and outside of the source catheter 12, oralternatively outside the applicator shaft or sheath, or still further,can comprise the applicator sheath itself. The end can be shapedarbitrarily to suit the situation at hand. FIG. 5 shows a truncated,obliquely angled tip 51 whereas FIG. 6 shows a window 61 which canoptionally have a sealed tip 62 (as shown). With such a shieldingapparatus, the materials of construction are preferably attenuating.

FIGS. 7 and 8 show applicator tips 71, 81 which have graduated levels ofshielding attenuation along their length by virtue of their geometry—themore distal, the less attenuating. In the embodiments shown, one tip 72is tapered (FIG. 7), and the other tip 82 stepped (FIG. 8). If thesource is positioned near the distal tip of the applicator, the radialradiation is more intense. if more proximal, the radiation is lessintense. The tip may be open (as shown) or optionally sealed to preventaxial emission.

FIG. 9 depicts a balloon applicator apparatus corresponding in part tothe applicator described in FIGS. 1 a, b, but having a balloon 100affixed to the shaft or sheath of the applicator 103 at point 102. Aconventional hub 101 is affixed to the proximal end of the applicatorshaft or sheath in order to provide for both source catheter 12introduction through the in-line port which is fitted with seals (notshown) to prevent balloon leakage past the catheter shaft, and forinflation of balloon 100 through the auxiliary port, a connecting lumenwithin the wall of the applicator shaft, and through a port in the shaftinto the balloon. The elements of the inflation circuit are not detailedsince they are standard within the industry.

FIG. 10 depicts a balloon applicator apparatus corresponding in part tothe applicator described in FIGS. 1 a, b, but having a balloon 100affixed to the shaft or sheath of the applicator 103 at point 102. Aconventional hub 101 is affixed to the proximal end of the applicatorshaft or sheath in order to provide for both source catheter 12introduction through the in-line port which is fitted with seals (notshown) to prevent balloon leakage past the catheter shaft, and forinflation of balloon 100 through the auxiliary port, a connecting lumenwithin the wall of the applicator shaft, and through a port in the shaftinto the balloon. The elements of the inflation circuit are not detailedsince they are standard within the industry.

FIG. 11 depicts a balloon applicator apparatus incorporating shieldingelements similar to those of FIGS. 4 a, b, but having a balloon 120affixed to the applicator shaft at point 121 on applicator shaft 122.Within applicator shaft lumen, but outside the source catheter 12, arethe two tubular shielding tubes 41 and 42 each having windows 43 and 44,and extending distally to be received by cup 124, providing rotatingfixation of the balloon 120 relative to the applicator axis at twopoints. At the proximal end of the applicator shaft is a conventionalhub 123. The source catheter and shielding tubes all pass concentricallythrough the straight port, with conventional seals (not shown) betweenadjacent parts to prevent balloon leakage. The auxiliary port is forinflation of the balloon 120 through a connecting lumen within the wallof the applicator shaft, and a port in the shaft into the balloon. Theelements of the inflation circuit are not detailed since they arestandard within the industry.

FIG. 12 depicts applicator apparatus having a truncated, oblique shieldsleeve 131 similar to that described in FIG. 5, but with a balloon 130affixed to applicator sheath 133 at a point 132. A conventional hub 134is affixed to the proximal end of applicator sheath 133 to provide forintroduction of the source catheter 12 and the shield sleeve 131, eachof which must be properly sealed. The auxiliary port is for inflation ofballoon 130 through this port, a connecting lumen within the wall of theapplicator shaft, and through a port in the shaft into the balloon. Theelements of the inflation circuit are not detailed since they arestandard within the industry.

FIG. 13 depicts applicator apparatus having a shield sleeve 141 withwindow, similar to that described in FIG. 6, but with its distal tipextended, and a balloon bonded or otherwise affixed to the applicatorshaft 143 at a point 142. The distal extension of shield sleeve 141cooperates with a balloon mounted cup 145 to provide a rotationalfixation between sleeve 141 and balloon 140, thus providing two pointballoon fixation as previously described. A conventional hub 144 isaffixed to the proximal end of applicator shaft 143 to provide forintroduction of the source catheter 12 and the shield sleeve 141, eachof which must be properly sealed. The auxiliary port is for inflation ofballoon 140 through this port, a connecting lumen within the wall of theapplicator shaft, and through a port in the shaft into the balloon. Theelements of the inflation circuit are not detailed since they arestandard within the industry.

FIG. 14 depicts a balloon applicator 148 having two alternate shieldingapparatus for preventing, or at least attenuating, radiation directedalong the applicator shaft 159, proximal of a balloon 150. To the rightis an attenuating portion 151 of the balloon itself. This portion can bean integral portion of the balloon, with a hub as shown, or alternatelywithout a hub, either molded in place or bonded to the balloon after oras part of fabrication, or as a segmental part of the balloon itself andincluded in the fabrication process. Preferably it is of polymer andfilled with attenuating filler as previously described and sufficientlyflexible so as to expand with the balloon upon inflation. To the left inFIG. 15 is a stand-alone flange 152 with collar 153 to affix the flangeto the applicator shaft, as an alternate embodiment. The flange is solidand is optionally movable along the applicator shaft 159 (see arrow) bya sliding fit tight enough to retain its set position, or alternatelyhaving a conventional clamp or bonded fastening. The flange material ispreferably a filled polymer, but could be metallic.

FIG. 15 depicts a balloon applicator 158 having a balloon 160 which inturn has an integral inflatable torus 161 located on an applicator shaft169 proximal of the main balloon 160. The torus 161 is preferably afilled polymer, acting as a radiation shield that is deployed as theballoon 160 is inflated.

The embodiment 168 of FIG. 16 is similar to that of FIG. 15, but in thisinstance, the torus 171 mounts on an applicator shaft 169 proximal ofmain balloon 170. With appropriate accommodation for inflation, as forexample by a separate tube outside the applicator shaft, the torus 171can be movable on shaft 169. It could also be fixed axially, and have aninternal inflation as has been described for the main balloons. Thistorus is also preferably of a filled polymer.

FIG. 17 shows an applicator 178 similar to the apparatus described inFIGS. 1 a, 1 b and FIG. 10, except that a segment 181 of the balloon 180is made attenuating by adding attenuating material to one portion of theballoon. The applicator is shown within breast tissue 178, and adjacentto a bone, in this example, a rib 182, with the attenuating materialsituated between the source 179 and the rib.

FIG. 18 shows an applicator 188 with balloon 190 and source 192 withinbreast tissue 19 and having a solid flange 189 as described in FIG. 14(to the left) mounted on the applicator shaft 191. The flange 189 inthis embodiment is shown slightly cupped to conform to the breastsurface. In other applications, the flange may optionally be shaped toaccommodate different anatomy.

An important feature of most of the above embodiments is that aradiation shield is included on an applicator, the shield havingradiation attenuating properties that vary with position. Such variationwith position includes positions beyond the shield, where no attenuationoccurs, and includes positions where a hole may occur in a shield, forzero attenuation at that hole or window. Thus, variation with positionis intended to include a simple shield wherein the x-ray source ispositioned so as to have its radiation attenuated by the shield orpositioned so as not to have its radiation attenuated.

The above described preferred embodiments are intended to illustrate theprinciples of the invention, but not to limit its scope. Otherembodiments and variations to these preferred embodiments will beapparent to those skilled in the art and may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A radiation brachytherapy applicator with directional shielding,comprising: an applicator with a shaft capable of being positionedwithin a living patient, the shaft having a lumen within which ispositioned an x-ray source, near a distal end of the applicator, aninflatable balloon connected to the shaft of the applicator so as to beinflatable after insertion to provide an expanded volume around thex-ray source, with the shaft including a balloon inflation lumen, and aradiation attenuating shield at the proximal end of the balloon, formedas part of the balloon and elastic so as to expand to form an increasingarea of attenuation as the balloon is expanded, to shield radiation inthe proximal direction and to form an increasing shielded volumeproximal of the shield as the baloon is expanded.
 2. A radiationbrachytherapy applicator with directional shielding, comprising: anapplicator with a shaft capable of being positioned within a livingpatient, the shaft having a lumen within which is positioned an x-raysource, near a distal end of the applicator, an inflatable balloonconnected to the shaft of the applicator so as to be inflatable afterinsertion to provide an expanded volume around the x-ray source, withthe shaft including a balloon inflation lumen, and a radiationattentuating shield on the shaft entirely proximal to the balloon, theshield being inflatable by an inflation fluid so as to shield radiationin the proximal direction to an increasing extent and over an increasingvolume as the shield is inflated.
 3. (canceled)
 4. An applicator as inclaim 2, wherein the shield is inflatable separately from the balloon.5. An applicator as in claim 4, wherein the shield comprises aninflatable torus mounted on the shaft for axial sliding movement, so asto be selectively inflatable and selectively positionable relative tothe source and balloon.
 6. A radiation brachytherapy applicator withdirectional shielding, comprising: an applicator with a shaft capable ofbeing positioned within a living patient, the shaft having a lumenwithin which is positioned an x-ray source, near a distal end of theapplicator, a radiation attentuating shield mounted slidably on theexterior of the shaft and limited to a path of sliding travel having amost distal position spaced proximally of the x-ray source, so as toshield radiation in the proximal direction, so that the shield isadjustable as to distance from the x-ray source.